This invention relates to polyphosphazene copolymers containing repeating ##STR3## units in the polymer chain in which substituents derived from pyruvate esters and other compatible substituents are attached to the phosphorus atom. More particularly, the invention relates to copolymers containing substituents having the structure ##STR4## and other compatible substituents in which the substituents derived from pyruvate esters serve as curing or crosslinking sites for the copolymers.
Polyphosphazene copolymers containing small amounts of certain unsaturated substituents which are capable of undergoing further reaction (i.e. crosslinking) at temperatures ranging from 200.degree. to 350.degree. F. are described in U.S. Pat. Nos. 3,702,833; 3,844,983; 3,888,799 and 4,055,520. As described in the aformentioned patents, these reactive unsaturated substituents may be unsaturated monovalent radicals such as --OCH.dbd.CH.sub.2 ; --ORCH.dbd.CH.sub.2 ; ##STR5## --ORCF.dbd.CF.sub.2 and --OCH.sub.2 RF.dbd.CF.sub.2 where R is an aliphatic or aromatic radical.
The copolymers described in the above patents exhibit a member of advantageous properties as a result of the inclusion of small amounts of the above described unsaturated substituents therein. Thus, the copolymers when crosslinked are useful as solvent and chemically resistant coatings, sealant, potting compounds and so forth. However, the copolymers of these prior art patents require elevated temperatures i.e., 200.degree. to 350.degree. F. to affect crosslinking.
In contrast, the copolymers of this invention contain as the cure site substituents derived from pyruvate esters which permits crosslinking or curing of the copolymers at room temperature. Alternatively, the copolymers may be cured at elevated temperatures, if desired.